Oxidation of polynuclbar aromatic hydrocarbons



Patented Feb. 9, 1932 ALPI'ION S O. JAEGER, OF

MOUNT LEBANON, PENNSYLVANIA, ASSIGNOR TO THE SELDEN COMPANY, OF IITTSBURGH, PENNSYLVANIA, A CORPORATION OF DELAWARE OXIDATION OF POLYNUCLEAE AROMATIC HYDROCARBONS No Drawing.

This invention relates to the catalytic vapor phase oxidation of polynuclea-r aromatic compounds.

in the catalytic oxidation of polynuclear aromatic hydrocarbons in commercial quantities it has always been necessary to con sider two opposing factors in determining the most economical operatii'ig conditions. These factors, which vary more or less independently of each other in accordance with the kinetics and thermodynamics of the procthe relative value of raw materials and finished product and the permissible plant operz'iting expenses, are the percent 'c yield obtained from the raw material and the rate of conversion or output of the converters. When reaction temperatures are maintained at the lower part of the operative range, higher percentage yields are usually obtaiued and this method of working is usually indicated in cases where an expensive raw material is to be oxidized or one which refuires expensive purification. treatment. ()n the other hand, it is frequently necessary to oxidize a considerable portion of a cheap raw material such as naphthalene to carbon dioxide and water in order to obtain ti '2 greater output which is possible by the use of higher trunperatures.

It will be seen, however, that a material saving could be effected in oxidizing any type of hydrocarbons it higher reaction velocities and greater outputs per unit of time could be obtained without sacrificing the percentage yield.

The present invention is based upon the sur ju'ising discovery that it the reaction is split up into a number of parts the temperature conditions can be satisfactorily regulated to permit a shorter time oi contact without decreasing the percentage yield. This is efl'ected by passing vapors ot' the polynuclear aron'iatic compound admixed with an oxygcn-containing gas through a series of converters, the product being condensed out between converters and the exhaust gases containing the unrcacted portion of the compound to be oxidized being passed tl'irough the following converter. Remarkable increases in yield are obtained and under the Application filed. February 1'7, 1930. Serial No. 429,221.

most favorable circumstances it is possible to obtain conversion efliciencies of typical polynuclear aromatic compounds to intermediate oxidation products of more than 90%, which compares with production efiiciencies at commercial practical loadings of SO- 7.5% or less when a single converter is used.

The invention is in no sense limited to the use of any particular number of converters, the number used depending largely on the economics of the process; thus, for example, with an expensive raw material a larger number of converters can be profitably employed hau with a cheaper raw material Where the cag zital investment for converters and the labor cost is a relatively large item. A marked increase in efficiency is noted When as few as two converters are used in series, but I have found that it is desirable to use at least four converters in series. The production of the first three converters is about the smile, the fourth converter beginning to snow considerable falling off, and, of course, with a larger number of converters each additional converter gives a. proportionately smaller increase in yield. The number of converters which should be used is also to some extent dependent on the particular compound used the more delicate the reaction the larger the number of converters which will ordinarily be economically desirable.

While the present invention presents an iniportant improvement over the prior processes when fresh reaction gases are used in the first converter, it is desirable in order to get maximum yield to recirculate a part of the reacted gases. This may take place by pumping a. portion of the exhaust gases from the last converter in the series into the reaction gas stream entering the first converter, or, if desired, the recirculation can be for each converter in the series. Recirculation has a marked effect on the yield. Under ordinary conditions, for example, with a given catalyst and tour converters a conversion of anthracenc of somewhat more than 80% is obtained without recirculation. WVith recirculation of three-fifths of the exhaust gases from the last converter the production yield rises to better than 85%. It should be noted, however, that if the catalyst is loaded to such a point that the production is as high as the catalyst can give, recirculation does not seem to raise the yield any. This would indicate that the recirculation primarily-prevents destruction' of the product already formed, but does not aid in accelerating the oxidation of the side chain compound itself. It should be understood, however, that this is not definitely proven, and it is possible that other factors may be involved, and, accordingly, the invention is in no sense limited to any theory of action of the recirculation and, of course, is not-limited to recirculation, which constitutes merely a preferred embodiment.

. The present invention is applicable generally to the oxidation of all polynuclear aromatic compounds, such as naphthalene to phthalic anhydride, anthracene to anthraquinone, phenanthrene to phenanthraquinone and fluorene to fluorenone. The benefits of the invention are applicable to all of these reactions, as well as to those involving homologues and substitution products of the raw 'materials mentioned.

The present invention is not limited to any particular type of converters, but it is advantageousto maintain uniform temperaturesand, therefore, converters having relatively small catalyst compartments, such as, for example, tubular converters whose temperatures are controlled by baths, either boiling or nonboiling, can be very effectively employed. Although the invention is in no sense limited to their use and other types of converters, such as reaction gas-cooled converters, and the like, may be used. 7

Iron converters tend to form layers of iron oxide, which appears to act as a combustion catalyst and increases losses due to destruction of the oxidationproduct. It is, therefore, desirable to inactivate the converter walls coming in contact with the reaction gases, either by using special steels or other metals which do not form oxides of iron under the reaction conditions or by coating the walls with a compound of an alkali, alkaline earth, or earth metals which forms a layer which is not a combustion catalyst. Of course, the invention is not limited to converters thus inactivated, this being merely an advantageous feature in the preferred modification.

The temperature at which the reaction takes place may be varied within considerable limits, good results being obtained in the case of bath-cooled converters and bath I temperatures between 370 and 4:60" C. It should be understood that the temperatures will vary somewhat with the nature of the catalyst, but in general the conversion temperatures will be higher when a plurality of converters are used employing shorter catalyst lengths than when the entire reaction is caused to take place in a single converter. The invention is, however, in no sense limited to the temperature ranges given above, which constitute merely the preferred ranges.

The amount of fresh air used may be varied within wide limits, for example proportions of 1:20 to 1:40 by weight may be found desirable. In general the amount of fresh air will be less where the portion of recirculated airis greatest, but this depends-to a considerable extent on the loading and on the nature of the catalysts. The invention is in no sense limited to the ranges given.

In most installations fresh vapors of the side chain aromaticcompound enter onlythe first converter of the series. This type of installation presents advantages from the equipment standpoint, but the invention is not limitedto such constructions and it is;

included within the scope of the present invention, and for some'of the reactions covered by the invention they present important advantages in higher yield and smoothness of control.

The invention will be illustrated in greater detail" in connection with the following specific examples, which-are illustrative embodiments only.

E wample 1 Three converters of the boiling bath type are. arranged in series with catalystheights of 304:0 cm. The converters are filled with catalyst consisting of a diluted base exchange body, the diluents being impregnated with ferric. oxide and incorporated into the base exchangebody during itsformationas described in Example 8 of my 'Patent No. 1,694,620, dated December 11,. 1928. The catalyst is maintained at 380-400 C. by means, of the bath and a mixture of anthracene and air in a proportion of 1: 40 is passed over the catalyst. The anthraquinone produced in each converter is condensed out before the gases are passed into the next one and a total yield of around 859()% is obtained.

EmampZeZ Converters are set up as described in Example 1 and filled with a phthalic anhydride catalyst prepared by spraying etched quartz fragments heated to 400 C. with a concentrated solution of'ammonium vanadate, the particles being turned continuously to ensure an even coating. Vaporized naphthalene ,mixed with air in the ratio of 1:15-20 is passed through the catalyst. at temperatures of 400' 4QO C., thetemperature in the'first converter being slightly lower than the others,

and phthalic anhydridc is condensed out between each pair of converters. Yields of Sill- 85% ot theore 'ical are obtained, with the added advantage that higher gas speeds may be used.

Example 3 Com-'crters are set up as in Example 2, but are iillcd with a catalyst prepared in accordance with Example 3 or" my copending application Serial No. %,614, filed Sept. 7, 1928. Acenaphthene of 85% purity is vaporized with air and steam in the proportion of 1: 10 by weight and passed through the converters at 590-400 6., naphthalic anhydride of good purity being; condensed out between each pair of converters. Yields amounting to 85% of theoretical are obtained.

hat is claimed as new is:

1. A method of oxidizing at least one of the nuclei of polynuclear aromatic hydrocarbons, which comprises vaporizing the hydrocarbons. a dmixing them with an oxygen contaii'iing gas, and passing the mixture at reaction tmnperaturcs through a series of converters containing a catalyst favoring the oxidation of at least one of the nuclei, the reaction mixture being passed through the first converter at a speed in excess of that pi-n'mitting oxidation of all of the polynuclear aromatic hydrocarbon, the converted prod not being condensed out after leaving each converter, and nncondensed gases passing in series through the next converter.

:2. A method according to claim 1. in which at least a portion of the. exhaust ses from the last converter in the series is recirculated into at least one other converter of the series.

3. A method according to claim 1, in which at least a portion of the exhaust gases from the last converter in the series is recirculated into the first converter of the serir d. A method of oxidizing at least one of the nuclei of polynuclear aromatic hydrocarbons, which comprises vaporizing the hydrocarbons, admixing them with an oxygen con taining gas, and passing the mixture at reaction temperatures through at least three converters in series containing a catalyst favoring the oxidation of at least one of the nuclei, the re action mixture being passed through the tirst converter at a speed in excess of that permitting oxidation of all. of the polynuclear aron'iatic hydrocarbon, the converted product be ing condensed out after leaving each converter and uncondensed passing in series tl'irough the next converter.

5. A method according to claim 1, in which the catalyst contains associated with the effective component at least one compiinuxl of the group comprising alkali metals alkaline earth metals, and earth metals whose oxides are not reducible with hydrogen.

6. A method of oxidizing a trinuclear aromatic hydrocarbon, which comprises vaporizing it, admixing the vapors with an oxygen containing gas, and passing the mixture at reaction temperatures through a series of converters containing a catalyst favoring the oxidation of at least one of the nuclei, the reaction mixture being passed through the first converter at a speed in excess of that permitting oxidation of all of the trinuclear aromatic hydrocarbon, the converted product being condensed out after leaving each converter and uncondensed gases passing in series through the next converter.

7. A method according to claim 6, in which at least a portion of the exhaust gases from the last converter in the series is recirculated into at least one other converter of the series.

8. A method according to claim 6, in which at least a portion of the exhaust gases from the last converter in the series is recirculated into the first converter of the series.

9. A method of oxidizing atrinuclear aromatic hydrocarbon, which comprises vaporizing it, admixing the vapors with an oxygen containing gas, and passing the mixture at reaction temperatures through at least three converters in series containing a catalyst favoring the oxidation of at least one of the nuclei, the reaction mixture being passed through the first converter at a speed in excess of that permitting oxidation of all of the trinuclear aromatic hydrocarbon, the convcrted product being condensed out after leaving each converted, and uncondcnsed gases passing in series through the next converter.

10. A method according to claim 6,111 which the catalyst contains associatedwith the etiective component at least one compound of the group comprising alkali metals, alkaline earth metals, and earth metals whose oxides are not reducible with hydrogen.

11. A method according to claim 1, in which the temperature is between 380 and 450 C.

12. A method according to claim (3, in which the temperature is between 380 and 420 C.

13. A method of producing quinones from polynuclear aromatic hydrocarbons, which comprises vaporizing the hydrocarbon, admixing it with an oxygen containing gas and passing the mixture in series through a plurality of converters filled with a catalyst favoring the oxidation of at least one of the nuclei to the corresponding quinone at a temperature of approximately 380l20 0., the reaction mixture being passed through the first converter at a speed in excess of that permitting oxidation of all. of the polynuclear aromatic hydrocarbon, the converted product being condensed out between each pair of converters.

14. A method according to claim 13, in which at least part of the exhaust gases from the last converter is recirculated into the in take of at least one converter earlier in the series. 7

15. A method according to claim 13, in which at least part of the exhaust gases of the last converter is recirculated into the intake of the first converter.

16. A method of producing an anthraquinone from an anthracene substance, which comprises vaporizing the anthracene substance admixing it with an oxygen containing gas and passing the mixture in series through a plurality of converters filled with a catalyst favoring the production of anthraquinones from anthracenes at a temperature of approximately 380-150 C.',- the reaction mixture being passed through the first, converter at a speed in excess of that permitting oxidation of all of the anthracenes, the converted product being condensed out between each pair of converters.

17. A method according to claim 16, in which at least part of the exhaust gases from the last converter is recirculated into the intake of at least one converter earlier in the series.

18. A method according to claim 16, in v which at least part of the exhaust gases of the last converter is recirculated into the intake of the first converter.

19; A method according to claim 1, in which the fresh vapors or the polynuclear aromatic hydrocarbon are introduced directly into at least one converter of the series other than the first converter.

20. A method accordingto claim 16, in which fresh vapors of the anthracene substance are introduced directly into at least one converter of the series other than the first converter.

Signed at Pittsburgh, Pennsylvania, this 6th day of February, 1930.

ALPHONS O. JAEGERJ 

